A display panel such as a transmissive or transflective liquid crystal display panel requires a back-lighting source for illumination. For a large display panel, a plurality of lamps are commonly used for such purposes. A back-lighting source using one or more lamps is known in the art. For example, a back-lighting driver circuit having an inverter driver can be used to drive a single lamp. As shown in FIG. 1, the inverter driver is used to convert a direct-current source VDC into an alternating-current source Vs to drive a single lamp. In the inverter driver circuit, a master transformer and a capacitor, together with a plurality of switches are used as a DC to AC converter. In order to reduce the driver cost when the back-lighting source has two or more lamps, a current balancing circuit is used instead. FIG. 2 is an example of prior art multi-lamp drivers. As shown, a current balancing circuit disposed between the inverter driver and a two-lamp light source is used to control the current to each lamp. As shown in FIG. 2, an inductor and a plurality of capacitors are used to balance the current in the two paths to the two-lamp light source.
Other commonly used current balancing circuits are schematically shown in FIGS. 3 and 4. As shown, electrical characteristics of passive elements such as capacitors, inductors and transformers are used to balance the currents among the multiple current paths to a multi-lamp light source. In these type of current balancing circuits, if the current in one current path is higher than the current in the other current path, the currents can be balanced out by channeling the differential current through the capacitor. The major disadvantage of these types of current balancing circuits is that each circuit can be used to provide only two current paths to two lamps. In a light source having N pairs of lamps, N current balancing circuits and a large number of inverter drivers are required.
It is advantageous and desirable to provide a method and device for driving N pairs of lamps with a smaller number of current balancing circuits and inverter drivers.